Introduction

ChessGrammar is a tactical pattern recognition engine for chess. Classification, not evaluation.

ChessGrammar is a specialized inference engine that detects, classifies, and explains tactical patterns in chess positions. It answers a different question than traditional engines: not "what is the best move?" but "what tactic exists here?"

What ChessGrammar does

Send a FEN position or a PGN game. Receive a structured list of every tactical pattern present — with the triggering move, target squares, material gain, and an optional forcing sequence.

{
  "tactics": [
    {
      "pattern": "fork",
      "trigger_move": "d4e2",
      "target_squares": ["g1", "c3"],
      "gain": 700,
      "is_mate": false,
      "sequence": ["d4e2", "g1g2", "e2c3"]
    }
  ],
  "count": 1,
  "depth": "l2",
  "performance_ms": 48.2
}

Classification, not evaluation

General-purpose chess engines (Stockfish, Leela Chess Zero) evaluate positions — they compute the best move and an evaluation score. They can find a fork, but they won't label it as a fork or explain why it works.

ChessGrammar classifies. Each detected pattern comes with a formal type label (fork, pin, skewer...), the pieces involved, and the material consequence. This makes it useful for:

Tactics trainers — auto-generate exercises from any game or position
Game analysis tools — annotate played games with tactical labels
Chess databases — tag and search positions by tactic type
EdTech platforms — explain chess tactics programmatically
Research — quantify tactical complexity across tournaments or players

Key characteristics

Property	Detail
Patterns	10 tactical patterns (fork, pin, skewer, discovered attack, double check, back rank mate, smothered mate, deflection, interference, trapped piece)
Depth modes	L1 (structural scan, ~13ms) and L2 (forcing tree confirmation, ~125ms)
Deterministic	Same input produces the same output, every time. No neural network variance.
Stateless	Pure REST API. No sessions, no state. One call per analysis.
Format	Accepts FEN (single position) or PGN (full game)

Developer Preview

ChessGrammar is currently in Developer Preview. The API is accessible without authentication, subject to rate limits (30 requests/minute, 3 game analyses/day per IP). The engine is actively evolving — new patterns and endpoints are being developed.

No API key is required during the preview period. Get in touch if you need higher limits.